OK, so a bit of a delay. I had been struggling holding tolerance with my ER32 collets and the block certainly wasn't sturdy for any substantial milling. I put an order in for a 5C collet fixture since I have a few collects and the 5C chuck for the lathe, just been using ER32 for so long and generally work stuff just isn't that critical. This little engine is certainly stretching my abilities, so its all good and will translate to better work when we get out of the current mess.
The crankshaft and crank webs have been giving me problems working them out and how to machine them. I finally came up with a plan, the CAD model below was early on and the counterweights have been reduced to hopefully match the spider and conrod estimated weights. As I wasn't happy with the ER32, stuff at this stage took a backseat whilst I finished another project that had been on the back burner. I got a little portable bandsaw, mainly for picking up stock that was too long for the car or I was offered a chunk if I could cut it off. My Clarke bandsaw had got too annoying for doing fiddly stuff and thought the portable saw would be good in an upright setting. The base is left over flooring and the table happened to be a bit of 4mm stainless plate, I probably couldn't have picked a worse material. It was horrendous to drill and cut. I laser cut 6 card templates getting the holes and slots lined up before coordinate drilling. I opted for a stiff table over ease of blade replacement, hence the torturous blade path but it does end up getting straddled by the fixings, meaning it won't flex.
After this and coming back to the engine, I made a start on my third spider not happy how the gudgeon pins were going to be fashioned. I cocked up at this stage and cut the blanks for the crank webs before thinking how I was going to hold them. I had also machined them to final diameter of 22mm, a size I don't have a 5C collet for, excellent planning. Put what was left of the 7/8" bar in the collet chuck and face each end (plan B) I can now machine the crank web details on each end of the bar and have plenty of material to grip.
The 5C fixture really came into it's own here. As a test I set a zero for doing the spider parts and then all operations based off that zero to see how much error I got on the 5C fixture. Happily none that was of concern, swapping collets between lathe and mill, and different sizes, very happy with the repeatability of this fixture. The milling of the counterweight was the part I had my doubts about, especially as I was using an 18mm end mill. Way bigger than I would normally use (thanks Rob) it munched it's way through the brass on each end.
Pleased with the results so far, new spider parts and crank webs done using the 5C collets, no fiddling getting them square and clocking parts up for runout. Finally for now, a test fit with the older two spiders to check fit and clearances, progress made still lots more to do on this adhoc build.